The number of radio access technologies available for uses such as cellular telephony and mobile broadband has grown rapidly in the later years. In the beginning of the 1990ies there were only a few standards available, such as NMT, GSM and IS-95, used almost exclusively for voice telephony. Currently, many additional radio access technologies (RATs) have been developed, such as W-CDMA, CDMA2000, EDGE, IEEE 802.16 and LTE, to mention just a few. There is also a demand for multi-mode terminals, for improved coverage and to be able to use the same mobile terminal when traveling, so that a single terminal must be able to use several RATs.
To add to this already heterogeneous situation, there is a regulatory interest to increase flexibility when it comes to spectrum allocations. An advantage of this increased flexibility is that the radio environment can be adapted to current usage patterns, so that the limited radio resources may be more efficiently exploited. For example, different RATs may be allocated to different frequencies in different geographical locations, and these locations and frequency allocations may also change over time.
Some ways of providing information on how to connect to the RATs which are present in a geographic region have been presented with the common name CPC (Cognition enabling Pilot Channel or Cognitive Pilot Channel). This is, for example, described in E2R II White Paper, “The E2R II Flexible Spectrum Management (FSM) Framework and Cognitive Pilot Channel (CPC) Concept—Technical and Business Analysis and Recommendations”. In a particular implementation of the CPC, the so-called outband broadcast CPC, the CPC is viewed as a RAT of its own using a particular predefined frequency, and an outband broadcast CPC transmitter broadcasts information on which RATs are available at different frequencies in the different locations covered by the outband broadcast CPC transmitter. In the solutions discussed today, different time slots are used for CPC information relating to different geographical areas, such that the information related to a particular area makes up only a small portion in time of the entire CPC broadcast. For example, a timeslot a can be used to transmit information on which RATs are available in an associated area A, timeslot b can transmit information related to area B, and so on. In one particular scenario of this approach, a coverage area of an outband broadcast CPC transmitter is divided in quadratic areas, so-called meshes.
Another new notion is so-called Dynamic Spectrum Access (DSA), which describes spectrum access where radio units are not limited to using fixedly allocated spectrum bands (such as their licensed spectrum), but rather adapt the spectrum bands and the RATs they use depending on conditions such as estimated throughput, latency requirements, spectrum availability etc. For instance, a communication system suffering from high load in its own licensed spectrum could dynamically access spectral bands owned by some other licensee to temporarily increase its throughput, as long as it does not cause unacceptable interference to the other licensee. As another example, a network of communicating nodes may change its operating frequency depending on current spectral conditions. Potentially, dynamic spectrum access can enable more efficient use of the limited radio spectrum resources. This is because several systems then share the same resources such that when one system requires only a small amount of spectrum, other systems experiencing higher loads can utilize a greater bandwidth.
A so-called hotspot is a device that that provides wireless communication services in a relatively small coverage area using low power transmissions, for example, compared with transmission powers used in a macro cell or similar. The coverage area of the hotspot is usually characterised by a high user density. The hotspot may, for example, be a WLAN access point, a pico base station or similar. With the introduction of more flexible and adaptable connection possibilities in user equipments (UEs) and an increasingly dynamic spectrum arena, the market for the introduction of local DSA capable hotspots becomes more attractive. A hotspot may, for example, by use of DSA mechanisms, obtain access to spectrum bands with more favorable propagation characteristics than what can be provided by, for example, today's unlicensed ISM (Industrial, Scientific and Medical) bands. Further, by novel spectrum techniques, the DSA hotspots may use discontiguous spectrum bands and/or channels and aggregate a large bandwidth allowing for very high data rates and capacity.
To connect to a conventional WLAN hotspot, UEs need to scan for WLAN access points in a specific frequency range. Even though the frequency band where the hotspot is operating and the RAT used are well known, this scanning is rather slow and power consuming. With the introduction of DSA, a UE wanting to connect to a hotspot has even less information on where, in frequency, to scan for the hotspot or on what RAT is used by the DSA hotspot. These additional degrees of freedom may significantly increase the average scanning time.
To be able to attract users to a hotspot such as e.g. a DSA hotspot, nearby UEs should be able to more quickly connect to the hotspot without a time and energy consuming spectrum scanning procedure. It may even be so that long average scanning times would discourage potential customers to search for the hotspot. An outband broadcast CPC transmitter with a large service area will most likely not be able to cope with many local DSA hotspots as this would generate too much information to broadcast, i.e., the time required to listen and decode the CPC information would be too long. Furthermore, the outband broadcast CPC approach requires some degree of UE positioning, since the UE needs to know which CPC information is relevant for its present location. A hotspot typically has a small coverage area, which means that the positioning would have to be rather precise. This may put the additional requirement of integrated GPS or a similarly precise positioning system in all UEs which are potential customers to hotspot services. Moreover, as the DSA hotspots change their operating frequencies and possibly adapt the used RAT to a local (in both time and space) spectrum situation, it will be difficult to keep this information updated in an outband broadcast CPC system. Finally, a hotspot owner may, for various reasons, not want to register their hotspot to the entity that manages the outband broadcast CPC. One reason for this may be that this entity could be managed by a competitor.
A problem addressed by the present invention is therefore to be able to overcome or at least mitigate at least one of the above-indicated difficulties.